1. Field of the Invention
This invention relates to a device for developing an electrostatic latent image formed on an imaging surface by applying a developing agent thereto and particularly to a developing device suitable for use in a recording machine, such as a copier, a facsimile machine and a printer, using magnetic toner as a developer agent.
2. Description of the Prior Art
FIG. 1 illustrates a typical prior art developing device using a so-called single component developer, or magnetic toner. As shown, adjacent to a photosensitive drum 1, whose outer peripheral surface defines an imaging surface on which an electrostatic latent image is formed according to any of the well-known electrophotographic image forming processes, is disposed a developing device 2 for developing the latent image formed on the photosensitive drum 1. The developing device 2 includes a hopper 3 for storing therein a quantity of a single component developer or magnetic toner 4, a sleeve 5 disposed rotatably at the bottom of the hopper 3, a magnet 6 disposed inside of the sleeve 6 for generating a magnetic field to cause the magnetic toner 4 to be attracted to the outer peripheral surface of the sleeve 5 and a doctor blade 7 formed by part of the hopper 3 for regulating an amount of toner 4 to be transported as carried on the sleeve 5.
In the above-described developing device, the magnetic toner 4 magnetically attracted to the sleeve 5 is regulated in amount by the doctor blade 7 and then applied to an electrostatic latent image formed on the photosensitive drum 1. As is well known in the art, the magnetic toner 4 becomes triboelectrically charged due to friction with the sleeve 5 and/or the docter blade 7 when formed into a layer on the sleeve 5. Alternatively, a charge injecting means may be provided to inject charge to the toner on the sleeve 5. The film of magnetic toner formed on the sleeve 5 is selectively transferred to the photosensitive drum 1 according to a charge pattern defined by the latent image on the drum surface. The toner remaining on the sleeve 5 after development is then transported back to the hopper 3 as the sleeve 5 rotates counterclockwise. Thus, fresh toner is supplied to those portions of the sleeve 5 where the toner has been used for developing the latent image. Such a structure is disadvantageous because a charge distribution becomes nonuniform thereby causing deteriorations in image quality, such as irregularities in density and background contamination.